There is a need in nonferrous pyrometallurgy to environmentally protectively convert high iron, nickel-cobalt and nickel-cobalt-copper mattes to low iron mattes in a single closed vessel, while discharging low value-metal containing slag and high sulfur dioxide containing off-gas. Since nickel ores all contain cobalt, increase in present practice low cobalt recovery is also important.
As an early and leading example of efforts in the above regard, the present co-inventor Queneau and Schuhmann "QS" continuous oxygen converter is a single vessel alternative to the standard chain of pyrometallurgical furnaces in series still used for the commercial production of copper, nickel and lead from their mineral concentrates and recycled materials. The QS converter is advocated as a replacement of current practice apparatus: sinter machines, blast furnaces, reverberatory, electric and flash smelting furnaces and Peirce-Smith converters, U.S. Pat. No. 942,346. Refer to P. E. Queneau and R. Schuhmann, U.S. Pat. Nos. 3,941,587; 4,085,923; and P. E. Queneau, "The Coppermaking QS Continuous Oxygen Converter, Technology, Design and Offspring", Extractive Metallura of Copper, Nickel and Cobalt, the Paul E. Oueneau, International Symposium: Volume 1, Fundamental Aspects, edited by R. G. Reddy, et al, pages 447-471, TMS, 1993. See also P. E. Queneau and S. W. Marcuson, "Oxygen Pyrometallurgy at Copper Cliff", pages 14-21, JOM, Volume 48, No. 1, January 1996, and P. E. Queneau and A. Siegmund, "Industrial-Scale Lead Making with the QSL Continuous Oxygen Converter", pages 38-44, JOM , Volume 48, No. 4, April 1996.
The QS converter is designed to accomplish continuous converting of copper, nickel, cobalt and lead mineral concentrates and recycled materials to metal or low iron matte, cleaning of the resulting slags and production of high strength sulfur dioxide off-gas, all in a single, countercurrent flow channel reactor, thus eliminating molten matte transfer. It's operations are carried out in a closed, fugitive emission-free, cylindrical, elongated, slightly sloped, tilting vessel. Overhead feeders and submerged Savard-Lee type gas injectors are employed to introduce metal sulfides, flux, oxygen and other gases, and carbonaceous material into the converter bath. The countercurrent matte-slag flow, concurrent gas--slag flow, smelting process utilizes the heat generated by the exothermic sulfur and iron oxidation reactions in the oxidizing zone, while generating a steady output of sulfur dioxide-rich gas. Low value-metal containing discharge slags are produced by submerged injection into the bath of oxygen and carbonaceous materials in the reducing zone for slag cleaning. The reactions generate a series of controlled oxygen potential regions in the bath, so that it progressively decreases in oxygen potential from product discharge to slag discharge. A key design concept of the QS converter is its length-long alternating, sequenced, chemically staged mixer-settler series of phase mixing by bottom blowing and phase separation by gravity settling. The principles of this converter are sound, but it is as yet only employed industrially for leadmaking.
Others have suggested a variety of methods conceived to solve the difficult problems associated with continuous pyrometallurgical conversion of metal sulfide concentrates to metal. In 1974 N. J. Themelis, U.S. Pat. No. 3,832,163, disclosed a coppermaking process and apparatus, known respectively as the Noranda process and Noranda reactor, characterized by continuous smelting and converting and concurrent flow of matte and slag, with most of the bath maintained in a high oxygen potential, turbulent state by oxygen-enriched air injection through the reactor's Peirce-Smith-type injectors. This bath smelting technology is employed industrially for the processing of high iron copper sulfide mineral flotation concentrates and copper-containing secondary materials to produce low iron-copper matte. The high value-metal containing slag produced requires separate treatment; air infiltration, and the gas injector design which limits the oxygen content of the bath oxidizing gas, decrease the sulfur dioxide concentration of the off-gas product. The new Kennecott Utah copper smelter employs a process which eliminates use of the Peirce-Smith converter. An Outokumpu flash smelting furnace produces low-iron copper matte from high iron copper sulfide mineral flotation concentrates. The molten matte is water-granulated, finely ground and dried, and continuously flash converted to blister copper in a Kennecott-Outokumpu flash converter. It's unconventional calcium ferrite slag is water-granulated and returned to the flash smelting furnace for value-metal recovery. The flash smelting furnace slag undergoes complex separate treatment for the recovery of its high value-metal content, and the concentrate produced is recycled back to the furnace. Both vessels employ oxygen-enriched air at 75-85% oxygen, and generate 35-40% S0.sub.2 off-gas. The overall process achieves a sulfur capture in excess of 99.9%. Refer to C. J. Newman et al, "Recent Operation and Environmental Control in the Kennecott Smelter", pages 29-45, COPPER 99-COBRE 99, Volume 5, Smelting Operations and Advances, edited by D. B. George, et al, TMS, 1999. See also D. B. George, U.S. Pat. No. 5,449,395.
Inco successfully improved batch vessel pyrometallurgical coppermaking operations by utilizing efficient sequences of oxygen flash smelter, oxygen top blown, nitrogen bottom-stirred reactor vessels. Refer to S. W. Marcuson et al., U.S. Pat. No. 5,180,423, and C. M. Diaz et al., U.S. Pat. No. 5,853,657. They teach the use of a converting process wherein nitrogen is sparged into a molten bath of sulfur-saturated copper through porous refractory plugs located in the bottom of a converter. The nitrogen effects mixing in the bath and forms a bath "eye" on its surface. This eye provides an open window for intense oxygen penetration of the semi-blister copper, since floating mush is locally removed. A top-blowing lance, disposed above the eye, directs oxygen into the stirred copper, oxidizing it effectively.
Present co-inventor Diaz and others have also advocated improved copper production from flotation mineral concentrates by alternative routes. One of these suggestions comprises three separate operations: roasting of a fraction of the copper concentrate feed, autogenous oxygen flash smelting of the calcine blended with the remaining concentrate fraction, to crude copper and separate cleaning of the resulting slag. Refer to G. S. Victorovich, M. C. Bell, C. M. Diaz and J. A. E. Bell, "Direct Production of Copper," pages 42-46, JOM, September 1987, and G. S. Victorovich, "Oxygen Flash Converting for Production of Copper," pages 501-529, Extractive Metallurgy of Copper Nickel and Cobalt. The Paul E. Oueneau International Symposium; Volume 1 Fundamental Aspects, edited by R. G. Reddy et al., TMS 1993, See also S. W. Marcuson et al., U.S. Pat. No. 4,830,667. Another route advocated consists of autogenous oxygen flash smelting of common copper concentrate to an intermediate grade matte, followed by the continuous conversion of this material to semiblister, with full recycle of the converter slag to the flash furnace, C. M. Diaz et al., Canadian Patent 2,074,678. The principles of these improvements are sound, but the concepts have so far not been used industrially.
An important need, commonly neglected in nickel smelting of both sulfide and oxide ores, is major improvement in cobalt recovery. For example it may require separate processing of large amounts of converter or primary smelting slags. In Peirce-Smith converting, finishing to mattes containing a substantial amount of iron permits higher cobalt recovery in the matte. However, due to the constraints of current nickel refining practice, iron levels generally must be kept low, thereby denying producers an optimum iron level that increases cobalt recovery.
The ancient Peirce-Smith converter, still a workhorse in the nickel and copper industries, has serious deficiencies that call for its retirement. There is thus great interest in developing a single, economical, high capacity, energy efficient, low polluting vessel that continuously produces low iron, nickel-rich matte from high iron, nickel-rich matte, while simultaneously improving value-metal recovery including cobalt, and sulfur fixation.
The present invention is a useful, novel combination of elements of the QS continuous oxygen converter, the INCO oxygen top blowing-nitrogen bottom stirring reactor technology, and additional important techniques. Inherent process inefficiencies and environmental problems of Peirce-Smith converter practice are remedied by employment of the present Queneau-Diaz ("QD") continuous nickel matte converter as defined below:
It is an economic, energy-efficient continuous oxygen reactor and process. The reactants are introduced to the closed reactor at well-defined steady state rates, while the finished product, slag and off-gas are continuously discharged, also at steady state rates. The continuous system permits and operates under comprehensive instrument process control of the reactor's physical (e.g., weights and temperatures) and chemical (e.g. staged bath oxygen potentials) conditions. PA1 When treating iron-rich, nickel-cobalt or nickel-cobalt-copper primary furnace mattes, the QD converter continuously yields low iron-containing matte, low value-metal containing, conventional iron silicate slag and high sulfur dioxide-containing gas, all superior to those produced in Peirce-Smith batch converter practice. The high iron content of the primary furnace matte is accompanied by furnace production of low value-metal containing discard slag. PA1 It eliminates fugitive emissions in the workplace and decreases the cost of off-gas sulfur fixation. PA1 It yields increased cobalt recovery of this valuable element. PA1 It optimizes the conditions for the establishment of highly effective, controlled chemical analysis bubble plumes in the reduction zone, by delivering pulverized bituminous coal to the submerged injectors by dense phase, uniform plug flow transport. The thus steady state higher oxygen concentration of the injected gas results in its lower momentum, improved heat and mass transfer in the bath, higher sulfur dioxide concentration in off-gas, and decreased operating difficulties in the atmosphere above the bath, thus increasing reactor capacity. PA1 It permits increased use of natural gas as a reductant for slag cleaning, by prior dispersion of a thermally minor quantity of highly reactive, combustible organic material in the gas.